Micellar-polymer flooding is well known. The cost is substantial and poor slug design can cause failure. Many publications relate to the various aspects of oil displacement with micellar systems. Exemplary of the literature in this area are the following references.
C. L. Stegemeier, in the chapter, "Oil Entrapment and Mobilization in Porous Media" in the book, Improved Oil Recovery by Surfactant Polymer Flooding, edited by D. O. Shaw, and R. S. Schechter, Academic Press, New York (1977) teaches that the mobilization recovery of tertiary oil is affected, at the microscopic level, by:
1. geometry of the pore network; PA1 2. fluid-fluid properties such as interfacial tension, density difference, bulk viscosity ratio, and phase behavior; PA1 3. fluid-rock properties, including wettability, ion exchange, and adsorption; and PA1 4. applied pressure gradient and gravity. PA1 R. N. Healy et al, Soc. Pet. Eng. J., 14, 491 (1974). PA1 W. B. Gogarty et al, Trans. AIME 243, 1407 (1968). PA1 J. L. Salager, et al, SPE Preprint No. 7054 presented at the Fifth Symposium on Improved Methods of Oil Recovery, Tulsa, April 1978. PA1 S. C. Jones et al, Soc. Pet. Eng. J., 16, 161 (1976). PA1 K. D. Dreher et al, J. Pet. Tech. 23, 1437 (1971). PA1 P. B. Lorenz et al, SPE Preprint No. 4751 presented at the Third Improved Oil Recovery Symposium, Tulsa (1974). PA1 (a) changes in the ratio of surfactant to hydrocarbon in U.S. Pat. No. 3,493,047 issued to J. A. Davis, Jr. et al, PA1 (b) increasing the concentration of cosurfactant within the microemulsion in U.S. Pat. No. 3,493,048 issued to S. C. Jones, PA1 (c) increasing the aromaticity of the hydrocarbon within the microemulsion in U.S. Pat. No. 3,495,660 issued to J. A. Davis, Jr. et al, PA1 (d) increasing the average molecular weight of the surfactant used to form the microemulsion in U.S. Pat. No. 3,500,912 issued to J. A. Davis, Jr. et al, PA1 (e) increasing the molecular weight of cosurfactant in U.S. Pat. No. 3,536,136 to S. C. Jones. PA1 Literature related to the subject is large and yet incomplete, since the mechanisms are complicated by interrelated properties of complex pore structure, fluid properties and applied conditions. Furthermore, the variability of oil reservoir rocks and fluids is so great that the most generalized conclusions have limited applicability. PA1 It is commonly known that the constituents of a micellar slug may interact in several ways with both the rock and the formation fluids when injected into a reservoir, and a considerable body of literature exists. In spite of this knowledge, however, it is not yet possible to design a micellar slug for tertiary oil recovery from basic principles because of the complexity of the phenomena and of inadequate understanding of the processes involved.
The article also notes that several mechanisms of oil displacement can be significant in micellar-polymer flooding. Opposing viscous and capillary forces are taught to be the controlling mechanism for simple two-phase systems. Other operating mechanisms include interphase mass transfer, interface aging effects, wettability changes and emulsification. At the microscopic level, variations in permeability, the presence of clays, the type of crude, etc. affect slug design.
Composition distinguishes the three types of micellar systems used in oil recovery. U.S. Pat. No. 1,823,439, issued to M. De Groot and U.S. Pat. No. 3,006,411 issued to O. C. Holbrook teach the use of dilute aqueous solutions of surfactants in oil recovery. This type of aqueous system may also contain small amounts of oil which may be no more than impurities in the surfactants and/or salts. U.S. Pat. No. 3,082,822, issued to W. B. Gogarty et al and U.S. Pat. No. 3,163,214 issued to A. K. Csaszar, teach the use of "soluble oils" which may contain varying amounts of water but which are mainly hydrocarbon and surfactant. The use of higher surfactant concentration microemulsions is taught in U.S. Pat. No. 3,254,714 to W. B. Gogarty et al, U.S. Pat. No. 3,506,070, U.S. Pat. No. 3,613,787 issued to S. C. Jones, and many others listed below. The microemulsions contain hydrocarbon, water, surfactant, and salts and may also contain cosurfactant.
There are major differences in opinion expressed within the literature regarding the need for phase stability in higher surfactant system floods. W. B. Gogarty et al teach that microemulsion integrity should be maintained as great a distance as possible during the flooding operation while R. N. Healy et al, Soc. Pet. Eng. J., 14, 491 (1974) and R. N. Healy et al, Soc. Pet. Eng. J., 15, 87 (1975) suggest that the microemulsion breaks down almost immediately and phase stability is substantially inconsequential.
The art contains many discussions of compositional factors. For example, R. N. Healy et al, Soc. Pet. Eng. J., 14, 491 (1974); Soc. Pet. Eng. J., 16, 147 (1976) and W. B. Gogarty et al, Trans., AIME, 243, 1407 (1968) note that salt has a marked effect on the phase behavior of microemulsions prepared with petroleum sulfonates. The effect of cosurfactant on phase behavior has also been discussed in a variety of papers:
The cosurfactants modify phase behavior and other physical properties of brine-hydrocarbon-surfactant systems. Changes in the molecular weight of cosurfactants can be quite important in determining phase behavior and physical properties. S. J. Salter, SPE. Preprint No. 6843, 52nd Annual Fall Meeting of the SPE, Denver, October 1977, teaches that there is a linear relationship between optimal salinity and alcohol content. Many surfactants have been taught to be useful. For example, see U.S. Pat. No. 3,254,714, issued to W. B. Gogarty et al; U.S. Pat. Nos. 3,506,070 and 3,613,787 to S. C. Jones; U.S. Pat. No. 3,997,451 issued to M. A. Plummer et al, and U.S. Pat. No. 3,888,309 to J. S. Rhudy et al.
Changes in composition change various physical and chemical characteristics of micellar dispersions. Thus, viscosity is regulated through controlling the amount of water in U.S. Pat. No. 3,275,075 issued to W. B. Gogarty et al. The concentration of water-soluble salts is used as a viscosity control in U.S. Pat. No. 3,330,343 issued to W. C. Tosch et al. The thermostability range of microemulsions is adjusted by:
Higher brine tolerances are obtained by using lower average equivalent weight surfactants and lower brine tolerances are obtained by increasing the average equivalent weight of the surfactant in U.S. Pat. No. 3,623,553 issued to D. N. Burdge. The hydrophil-lipophil balance is controlled to obtain desired formation rock wettability in U.S. Pat. No. 3,643,738 issued to K. D. Dreher et al. Stability at higher temperatures is increased by including in the microemulsion a cation which has a greater affinity for the petroleum sulfonate used to make up the micellar dispersion than the affinity of the cation within the interstitial water of the reservoir in U.S. Pat. No. 3,648,770 issued to R. D. Sydansk et al.
U.S. Pat. No. 3,687,201 to M. O. Son, Jr. et al teaches the control of the viscosity of an oil external microemulsion system by using relatively low average equivalent weight petroleum sulfonates to obtain relatively high viscosity microemulsions and relatively high average equivalent weight petroleum sulfonates to obtain decreased viscosities. The topic is generally discussed by L. A. Wilson, Jr. in the chapter, "Physical-Chemical Environment of Petroleum Reservoirs in Relation to Oil Recovery Systems" in the book, Improved Oil Recovery by Surfactant and Polymer Flooding, supra, p. 47. The use of various polymers in micellar polymers in micellar-polymer flooding is taught in many of the cited patent and literature references and several chapters of the cited Shaw et al book are directed to this subject.
There are other patents directed to additional aspects of slug design. These include, U.S. Pat. No. 3,307,628 issued to E. A. Sena, teaching a combination of oil and water soluble surfactants; U.S. Pat. No. 3,433,636 to W. B. Gogarty, teaching the desired mobility parameters for a slug; U.S. Pat. No. 3,476,184 to J. A. Davis, Jr. teaching modification of the composition and character of the microemulsion from front to back to control slug hydrophilicity; U.S. Pat. No. 3,507,331 to S. C. Jones wherein increased concentrations of some components are included within the leading edges of the microemulsion slug to insure stability; U.S. Pat. No. 3,976,582 to L. J. Douglas et al wherein Zeta potential is utilized for controlling or obtaining maximum oil recovery and U.S. Pat. No. 4,022,276 issued to K. D. Dreher wherein nuclear magnetic resonance measurements are used to obtain microemulsions designed to obtain maximum oil recovery.
Even when all of the implicit and explicit teachings of the large amount of art sampled above are considered, those skilled in the art find it quite difficult to design an optimum slug or other micellar system for use in oil recovery. This fact is confirmed by the recent failures of field tests of micellar-polymer floods where improper slug design and/or insufficient reservoir studies combined to insure failure.
The references cited above indicate some of the many approaches to micellar dispersions taken in the past. A plethora of other literature could be cited relative to other aspects of oil recovery using microemulsions and other forms of micellar flooding. However, the current state of the art relating to the design of a specific micellar system for a specific reservoir is summarized by G. L. Stegemeier, supra, p. 55, who states,
With reference to surfactant-flood systems made up of surfactant, water, oil, electrolyte, cosurfactant, etc., the state of the art may have been more succinctly summarized by Messrs. Walker and Ray of the University of Florida, Tham of the USERDA Bartlesville Energy Research Center and M. C. Lee of the Department of Chemical Engineering, Oklahoma State University, in their article, "Cation Exchange, Surfactant Precipitation, and Adsorption in Micellar Flooding", Symposium on Chemistry of Oil Recovery presented before the Division of Petroleum Chemistry, Inc., American Chemical Society, Anaheim Meeting, Mar. 12-17, 1978, wherein it was summarized.
The above indicates that the divergent courses taken by those skilled in the art as well as the chemistry and physics of the fluid-reservoir interaction may have served to obscure the pathway to inexpensive, effective slug design. The instant method will assist in remedying the problem.